In a recent study published within the journal Foods, researchers in Sweden evaluated the bacterial diversity, richness, and composition of 47 commonly available fermented foods corresponding to kimchi, kombucha, sauerkraut, water and milk kefirs, plant-based and regular yogurts, and fermented vegetables.

Study: Characterization of the Bacterial Composition of 47 Fermented Foods in Sweden. Image Credit: Created with the help of DALL·E 3

The Importance of Fermented Foods

Fermented foods are produced using microbes to enzymatically alter various food components, and the method not only preserves the food but in addition improves its dietary value and taste. Fermented foods have been consumed worldwide and are also often linked to realms and cultures. The recent popularization of fermented foods due to their health advantages has led to a wide selection of available traditional and commercially produced fermented foods.

Advancements in sequencing technologies have made it possible to simply discover and characterize bacterial communities. Bacterial communities can vary in size, complexity, abundance, and performance. Fermented foods are largely classified by the presence of lactic acid bacteria. Fermented foods from Asia, Africa, and Europe, including dairy products, kimchi, various kinds of kefirs, kombucha, and meat products, have been widely studied. Nonetheless, fermented foods’ microbial composition is dependent upon the starting ingredients and microbial community, and the identical foods might vary based on manufacturer, geographic location, and environmental aspects.

Study Design and Methodology

In the current study, the researchers investigated a wide selection of business and homemade fermented foods locally available in Sweden. They covered eight major fermented group types, namely, tibicos or water kefir, kombucha, milk kefir, sauerkraut, plant-based yogurt, fermented vegetables, and kimchi.

Data Collection and Microbial Evaluation

A complete of 47 homemade and commercially available fermented foods were collected or prepared, and for foods for which the data was available, data on starter cultures and bacterial composition was obtained. The homemade fermented foods prepared by the authors included sauerkraut, kimchi, yogurt, kombucha, water kefirs, plant-based yogurt alternatives, and milk kefirs.

Statistical Approaches

For the microbial evaluation, total deoxyribonucleic acid (DNA) was extracted, and polymerase chain response (PCR) was performed to amplify the V3 and V4 regions of the 16S ribosomal ribonucleic acid (RNA) gene. Amplicon sequence variants were identified, and people classified as mitochondrial or chloroplast sequences were faraway from the evaluation.

National Center for Biotechnology’s Nucleotide Basic Local Alignment Search Tool (BLAST) was used for the taxonomic task of the amplicon sequence variants, with reliable identification till the genus level. Moreover, the Inverted Simpson and Shannon diversity indices were calculated to find out the alpha diversity, and the richness was calculated after normalizing the amplicon sequence variant data.

The Kruskal-Wallis rank sum test was used to guage differences in richness and alpha diversity across the assorted fermented food groups, and the Wilcoxon rank sum test was used for pairwise comparisons to find out if the differences in richness and alpha diversity were statistically significant. Moreover, a principal coordinate evaluation was conducted to evaluate the dissimilarities in bacterial composition. Relative abundances were used to estimate the proportion of lactic acid and acetic acid bacteria in each fermented and fermented food group.

Key Findings and Results

The outcomes showed that a complete of two,497 amplicon sequence variants were retrieved and identified as belonging to 386 genera and 33 phyla. The richness and alpha diversity was found to differ significantly across various fermented foods and fermented food groups, indicating that the community structure of the bacteria present in these foods and people liable for fermentation varied widely.

Diversity in Industrial and Homemade Products

Two homemade and one business kombucha and one commercially available water kefir were found to have the very best richness and Shannon diversity, while plant-based yogurt alternatives and fermented vegetables were found to have the bottom richness and variety values. The kombucha and kefirs use a symbiotic bacterial and yeast culture, while the yogurts and fermented vegetables use a small and defined starter culture, which could explain the differences in richness and variety.

Dominant Bacteria Across Fermented Foods

The bacterial composition was primarily dominated by lactic acid or acetic acid bacteria, and a few bacteria were abundant across fermented food groups. Regular yogurt and plant-based yogurt alternatives had an abundance of Streptococcus thermophilus, while Lactiplantibacillus plantarum was present in large numbers in fermented cucumber, sauerkraut, and kimchi. Lactococcus lactis was present in one water kefir sample and most milk kefirs.

Graphical Abstract

Conclusions and Future Research

Overall, the findings reported that fermented foods varied significantly in bacterial composition, richness, and abundance, with some foods corresponding to kombucha and kefirs having very high richness and variety values and plant-based yogurt alternatives and fermented vegetables having lower bacterial richness and variety. The study highlights the necessity for further research to know the differences in product traits based on microbial communities and the impact of those foods on human health.